SiC-Si 3N4 Gradient Composite Ceramics by Special Hip Processing
α-SiC fine powder clad with special glass were sintered by HIP processing under 200 MPa at 1800 °DC. The density of material obtained is close to 97.5% of theoretical density, bending strength reached 582 MPa, which is about 50% higher than that of common pressureless sintered silicon carbide. After post-HIP treatment, density can be further increased to above 98.5% of theoretical density. The material with different composition can also be got in various atmospheres. According to thermodynamic calculation, SiC can be transformed into Si3N4 under optimum temperature and high N2-pressure. Experimental work was successful in fabricating SiC-Si3N4 gradient composite material. This kind of new SiC-Si3N4 gradient composite material were also identified by X-ray diffraction analysis. The strength and fracture toughness of this material is 900± 100 MPa and 8.4 MPa.m 1/2 respectively, which are about one times higher than those of hot-pressed SiC material. This study offered a new HIP processing technology for preparing high performance SiC-Si3N4 gradient composite ceramics directly from pure SiC powder.
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